Thermal Rearrangement of Osmabenzenes to Osmium Cyclopentadienyl Complexes

The chemistry of transition metal-containing metallabenzenes has attracted considerable attention.[1] Previous studies have led to the isolation and characterization of a number of stable metallabenzenes, especially those of osmium, [2][3][4] iridium, [5][6][7][8] platinum, [9] ruthenium, [10,11] and rhenium. [12] Many interesting chemical properties of metallabenzenes have also been discovered. For example, it has been demonstrated that metallabenzenes can undergo electrophilic substitution reactions, [2a, 5d] cycloaddition reactions, [8d, 9c] nucleophilic addition reactions, [13] and nucleophilic aromatic substitution of hydrogen. [14] Another common reactivity of metallabenzenes is that they can undergo migratory insertion reactions to give cyclopentadienyl complexes. The transformation has been demonstrated with well-characterized metallabenzenes [2e, 6b,-d,e, 10b] as well as a spectroscopically characterized ruthenabenzene, [15] and it has been proposed as a key step in the formation of cyclopentadienyl complexes.[1]Compounds closely related to metallabenzenes are metallabenzynes.[16] Compared with the chemistry of metallabenzenes, that of metallabenzynes is much less developed, which is partly due to the lack of convenient methods to synthesize such compounds.[17] Structurally, metallabenzynes are similar to metallabenzenes in that both have a delocalized structure. Thus it might be expected that metallabenzynes should have properties similar to those of metallabenzenes. Indeed, previous studies have demonstrated that metallabenzynes, like metallabenzenes, can also undergo electrophilic substitution reactions [18] and nucleophilic addition reactions.[17c] As formation of cyclopentadienyl complexes from metallabenzenes by migratory insertion reactions is well-known, one might expect that metallabenzynes could also undergo migratory insertion reactions to give carbene complexes. However, such reactions have not been previously observed. Herein, we present a reliable method to prepare osmabenzynes along with the first examples of conversion of metallabenzynes into carbene complexes.We recently observed that reaction of zinc with the osmium vinyl carbyne complex [OsCl 3 { C À CH = C(2-ClC 6 H 4 ) 2 }(PPh 3 ) 2 ] produced a osmanaphthalyne complex. [19] The reaction was proposed to proceed through a 16e fourcoordinate square planar osmium carbyne complex, which undergoes an oxidative addition reaction involving a CÀCl bond. Inspired by the observation, we envisioned that reactions of zinc with carbyne complexes of the type [OsCl 3 { C À CH = CR À CR' = CClR''}(PPh 3 ) 2 ] might lead to the formation of new osmabenzynes.To test this hypothesis, we first prepared the meridional osmium carbyne complex 1 and then treated it with zinc in THF at room temperature. An in situ 31 P NMR study showed that osmabenzyne 2 with substituents on the C3 and C5 positions was produced as the major phosphorus-containing product (Scheme 1), which can be isolated in 62 % yield after column chromatography.The osmabenzyne 2 has bee...

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Conversion of Metallabenzynes into Carbene Complexes

et al. 2011

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“…In particular metallabenzenes, which are organometallic compounds derived by the formal replacement of a C À H group in benzene with an isolobal transition metal fragment, have attracted considerable attention. [1] Previous studies have led to the isolation and characterization of an impressive number of stable metallabenzenes, especially those of osmium, [2][3][4] iridium, [5][6][7][8] platinum, [9] ruthenium, [10,11] and rhenium. [12] Metallabenzynes, [13] which are organometallic compounds derived from formal replacement of a carbon atom or a CÀH group in benzyne with an isolobal transition metal fragment, are closely related to metallabenzenes.…”

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confidence: 99%

Synthesis and Characterization of a Rhenabenzyne Complex

et al. 2011

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“…It is well known that metallabenzenes can undergo carbene migratory insertion reactions into cyclopentadienyl complexes. [17] A similar process can be detected in the isomerization of isometallabenzenes (Scheme 3). The proposed mechanism shows that it may go through the metalated cyclopentadiene intermediate B.…”

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confidence: 69%

Stable Iso‐osmabenzenes from a Formal [3+3] Cycloaddition Reaction of Metal Vinylidene with Alkynols

Zhao

Gong

et al. 2011

Angewandte Chemie

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The investigation on the synthesis and reactivity of metal vinylidene complexes has always been an active area, [1] especially given their applications as well-known catalysts for metathesis and carbon-carbon and carbon-heteroatom coupling reactions. [1b,e, 2] Compared with other reactions of metal vinylidenes, the cyclization reactions are underdeveloped. Previous studies showed that the vinylidene M = C a bond participated in cycloadditions (see a) as key steps in carboncarbon coupling reactions, [3] and some cycloaddition products have also been isolated. [4] Interestingly, similar reactions of the metal vinylidene C a = C b bond (see b) have been realized as well. [5] However, cyclizations of the skeleton of metal vinylidene (M = C a = C b ) as a unit (see c) remain scarce. In fact, the reported cyclization is a formal [3+2] cycloaddition reaction. [5c] To the best of our knowledge, the [3+3] cyclization reactions of metal vinylidene to construct six-membered rings have not been reported.Moreover, since the first isolation of metallabenzene was achieved by Roper and co-workers, [7a] considerable research interest has been attracted in this field. [6,7] Nevertheless, the metallabenzene analogue isometallabenzene, which can be seen as a metal-containing 1,2,4-cyclohexatriene, has not been thoroughly explored. Until now, only the 16e À isometallabenzene[Os{ = C = C(Ph) À CH(Ph) À CH = C(CH 2 Ph)}Cl-(PiPr 3 ) 2 ], prepared by double coupling reactions, was reported by Esteruelas and co-workers in 2004. [8] Herein, we report an unprecedented formal [3+3] cycloaddition reaction between the hydride vinylidene complex [OsHCl 2 -{=C=CH(PPh 3 )}(PPh 3 ) 2 ] (2) and alkynols under mild conditions to give stable 18e À iso-osmabenzenes. The origin of the unexpected stability of these iso-osmabenzene complexes and their isomerization into h 5 -cyclopentadienyl complexes through metalated cyclopentadiene intermediates is also described.Stirring of the osmium hydride alkenylcarbyne complex [OsHCl 2 ( C À C(PPh 3 ) = CHPh)(PPh 3 ) 2 ]BF 4 (1) [9] in a mixture of H 2 O/CH 3 OH (3:2 v/v) at reflux produced the osmium hydride vinylidene complex 2, which was isolated as a lightyellow solid in 60 % yield (Scheme 1). The other product, PhCHO, was detected by 1 H NMR (d = 9.3 ppm; PhCHO) and GC analysis of the reaction mixture (see Figure S1 in the Supporting Information). Complex 2 was characterized by NMR spectroscopy and elemental analysis, and the structure was additionally confirmed by single-crystal X-ray diffraction ( Figure S2).Complex 2 is thermally stable in the solid state but highly reactive in solution. Treatment of 2 with HC CCH(OH)Ph in dichloromethane or chloroform at room temperature led to a fast color change from light yellow to brown red. The unexpected iso-osmabenzene 3 was generated from a formal [3+3] cycloaddition and isolated in high yield (93 %). Similarly, when 2 reacted with HC CCH(OH)CH = CH 2 or HC CCH(OH)CH 2 CH 3 under the same reaction conditions, the other two iso-osmabenzenes, 4 (88 % yield) and...

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Thermal Rearrangement of Osmabenzenes to Osmium Cyclopentadienyl Complexes

Cited by 47 publications

References 25 publications

Conversion of Metallabenzynes into Carbene Complexes

Conversion of Metallabenzynes into Carbene Complexes

Synthesis and Characterization of a Rhenabenzyne Complex

Stable Iso‐osmabenzenes from a Formal [3+3] Cycloaddition Reaction of Metal Vinylidene with Alkynols

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